jetranger-RCU

My Feedback: (1)

Say a 2 cell lipo 2000 mah. At full power say motor draws 10 amps runs for 10 minutes. Now the 3 cell 2000 mah lipo, if you power back so the volts are the same as the 2 cell at full power, and draws the same amps, will the pack run out in 10 minutes. Or will the extra 4 volts ad to run time?? My guess is the same time.

Fliprob17

They wind up giving you the same run time, but the 3 cell has a much higher voltage output to the motor, so you wind up with more overall power, or watts, than you would with a 2 cell.

Example: 2 cell 7.4 volts x 10 amps = 74 watts ---- 3 cell 11.1 volts x 10 amps = 111 watts

The only real difference, besides voltage obviously, is the weight of the pack. The 3 cell is going to weigh more than the 2 cell if they are both 2000mah. Just depends on how many total watts you need for performance. That will tell you if you can get away with a 2 cell, or if you need the 3 cell.

For arguement sake, you would probably be able to run the 3 cell at a lower throttle setting (less amps) than the 2 cell to get the same performance, since the voltage is higher, leading to more watts. So I would suppose the 3 cell might actually give you a little longer run time. Depending on how much throttle you need. Using the example above, you could run the 3 cell setup at about 2/3 the throttle, or 6.6 amps and still match the 2 cell in terms of watts.

mrasmm

well depends on how you do it, if you're talking about the same performance with the extra weight, it might last a bit longer, maybe up to 20% or so, of course depending on what it's in.

If you are talking about cutting it down to the same voltage so it draws the same amperage as the 2s lipo, it will last 50% longer.

jetranger-RCU

My Feedback: (1)

The reason I asked this is,I know the 3 cell will give more power. But if the plane flys perfect on 2 cells. I was thinking may be 3 at the same power level would extend the flight time with the extra few volts???

Fliprob17

Even with the added weight of the 3 cell, since you will be able to run at a lower throttle setting with it, and run less amps, you should theoretically get more run time.

jooNorway

Some wrong therms here... Volts will never be the same, the 3S have a higher voltage. But instead of flying at full power as you did with the 2S, delivering 75Watt, you throttle back with 3S to deliver the same amount of WATT, not volt. Since "Watt=voltxAmp" and your voltage is higher from a 3S the amperes will be lower giving more flighttime.
As already mentioned; you get extra weight and might need some more watt to fly. Also remember; when you put in a 3S the propeller usually have to be smaller to avoid ruining the motor and ESC Maybe you put on a propeller whch make your setup still deliver 75Watt at WOT, but amperes are no longer 10A but 6,7A. ViolĂ*, 50% more flighttime.

mrasmm

=)

that's what I was saying, probably around 20% longer (but maybe more), but it could theoretically be upwards of 50% and with the 3s it would definately have more power for punch outs and what not

aman_74

How do you go from 2s to 3s and cut the voltage down to what the 2s had?

mrasmm

what I was meaning is making it so the total RMS voltage/amperage of the ESC was = the 2s. In otherwords, running the plane at a lower throttle.

In this case though it will not fly quite as well because you have added an additional 50% to the battery weight, that is where the redection comes off of the 50% theoretical number

hopefully that made it as clear as mud [sm=tongue_smile.gif]

gittarpikk

Lol... as electrician would look at it..

2000 mah is exactly that 2000 mah...the total capacity that can be delivered to the motor...no matter what voltage or cells there are.
so no matter what the voltage you run... if you throttle back to equal the same power(a direct function of watts...ie voltsXamps) then it makes sense that the battery will run out at exactly the same time.

I see the pack weight the same theoretically if the cells are proportionately smaller in the 3 cell to keep the mah the same.

I see the (ability) to burn up a larger amount of watts on demand..(reducing) the runtime if so done....as only 2000 mah are available...and when watts are raised, the the reserve is lowered.

make sense?